I think lactate, although a non-specific test, can help identify patients at risk of early decompensation. I think this is especially true in elderly who have nonspecific complaints (confusion, AMS, weakness the list goes on). In addition, although EGDT classifies patients with lactate >4 into one category, clearly there is a non-linear relationship in terms of outcomes. For example, a lactate of 4.5, is not the same as a lactate of 9, and as you start getting lactates that high it's usually do to a seizure, or severe ischemia somewhere.
I order lactate routinely on elderly patients who by history I am not sure what is going on, or if it is indicated by the history (abdominal pain concern for mesenteric ischemia, sepsis, etc... I also order it in patients with sepsis with a repeat in 2-3 hours to check how my resuscitation is going, i.e. clearing > 10% (I don't have the luxury of admitting to ICU within 2-3 hours, almost ever.)
In comparison to other tests like, BNP which has somehow crept into being ordered routinely in patients with shortness of breath, I think lactate gives me some prognostic value as well as helps tell me if I need to keep searching for another cause I haven't yet thought of, despite it being a non-specific test.